Colons, Semicolons & Em Dashes

Form

Colons, semicolons and em dashes each do a job that a comma or a period cannot.

A colon introduces whatever the clause in front of it has promised, which may be an explanation, a list or a single word (There was one problem: money). A semicolon joins two complete sentences that belong together without a conjunction, and it also separates list items that already contain commas (Sales rose; costs rose faster). An em dash adds emphasis in place of a colon or a pair of commas (The answer — surprising as it was — was obvious).

When to Use It

1. 1

   Introducing an explanation after a complete clause, with a colon

   There was only one thing stopping us: money.

2. 2

   Introducing a list after a complete clause, with a colon

   We hired three specialists: a designer, a developer, and an analyst.

3. 3

   Joining two closely related complete sentences, with a semicolon

   The meeting ran two hours over; nobody seemed to mind.

4. 4

   Separating list items that already contain commas, with a semicolon

   The speakers came from Tokyo, Japan; Lagos, Nigeria; and Lima, Peru.

5. 5

   In front of a transition such as however or therefore, with a semicolon

   The presentation went well; however, the questions were hard.

6. 6

   Setting off an emphatic aside, with a pair of em dashes

   The new director — despite her lack of experience — has made a real impact.

Common Mistakes

• A colon after an incomplete clause: write She loves reading, cooking, and hiking, not She loves: reading, cooking, and hiking — inside a sentence, the words in front of a colon should form a complete clause.
• A semicolon plus a conjunction: write She was tired, but she kept going, not She was tired; but she kept going — the semicolon already joins the two sentences, so it rarely needs a conjunction after it.
• A semicolon in front of a fragment: write He gave one answer: yes, not He gave one answer; yes — when a semicolon joins two statements, each side has to be a complete sentence.
• A hyphen in place of an em dash: write The answer — surprising as it was — was obvious, not The answer - surprising as it was - was obvious — an em dash is the long one; a hyphen only joins words.
• A capital letter after a colon: write There was one problem: money, not There was one problem: Money — what follows a colon starts lowercase unless it is a proper noun (some styles also capitalize a full sentence).